Singapore nuke summit with Kim is on, says Trump

President Donald Trump has said an unprecedented nuclear arms summit with North Korean leader Kim Jong Un that the US pulled out of will now go ahead as scheduled on June 12 in Singapore.

"I think it's probably going to be a very successful, ultimately a successful process," Trump said on the White House lawn after meeting a North Korean official in the Oval Office.

Kim Yong Chol, a close aide to the North Korean leader, delivered a letter from his boss to Trump.

The envoy was the highest level figure from the secretive state to hold talks at the White House since a senior envoy visited former president Bill Clinton in 2000.

Softening

Trump first told reporters the letter from Kim was "a very nice letter ... a very interesting letter", but then said he had not opened it.

The president appeared to significantly lower expectations for the outcome of the historic summit, frequently describing it as the start of a process and not the place where the two leaders were likely to sign any agreement. He said a number of summits might be required.

"Frankly, I said, 'Take your time,'" Trump said.

It was an extraordinary softening of tone towards North Korea from a president who last year threatened to rain "fire and fury" on the country because of the threat its nuclear weapons and long-range missiles pose to the US.